Anyway, I'm a guitarist as of now, and with guitars, 3 preamp tubes and 4 power amp tubes is something you'd expect on a 50 watt amp. How is it so radically different with this amp, that it can use such a small number of tubes to get so much power? Is this universal with all bass amps, or just this specific model?

If you feel like talking alot of posting stuff that's barely on topic, please do, I want to learn as much as I possibly can, even if it isn't directly on topic or a very in-depth explanation.

Hi Jacob, the power level is primarily determined by the "type" of tube. In y'r average 50-watt guitar amp, Fender uses a pair of 6L6-type tubes, which are rated at a maximum dissipation of around 25 watts, so a pair of them can crank out 50 watts. "Most" 50-watt tube amps use a pair of 6L6's, the lower power ones (like the Deluxe and Princeton and so on) use a pair of 6V6's, which can only crank out about half as much power as the 6L6's (hence the 20-watt ratings on these amps).

For bass amps, there are two solutions to get higher power: either a) use "more" 6L6's, or b) use higher power tubes. The Mesa 400 uses option (a), they put "lots" of 6L6's in the circuit to get more power (note that typically, the 100 watt guitar-type amps will use four 6L6's instead of two, and so on). On the other hand, the SVT and the YBA200 use option (b), they use higher power tubes.

The 6550 is a different tube. It can dissipate more power (around 50 watts), and it's also physically bigger. Of the various brands of 6550's (both current production and NOS), the GE 6550A is probably the best sounding for instrument amps, followed by the Svetlana "Winged C". 6550's are also used in many of the popular Marshall amps (although the Plexi types use EL-34's, which is "yet another" type of output tube). The Marshall Major, for instance, runs four 6550's, resulting in a total power output of just over 200 watts. That sounds like a very similar arrangement to your Traynor amp.

Of the various brands of 6550's (both current production and NOS), the GE 6550A is probably the best sounding for instrument amps, followed by the Svetlana "Winged C".

Click to expand...

I guess like anything, opinions vary. I'm researching 6550/KT88/KT90 to load in my soon to be aquired Peavey Classic 400 (uses 8x 6550 power tubes 400watts!!!) and have read & been told to stay away from current "Winged C" tubes.

I think I've made my choice with the Electro Harmonix 6550 but am still thinking the EH KT88 may be bought.

The 6550 is a different tube. It can dissipate more power (around 50 watts), and it's also physically bigger. Of the various brands of 6550's (both current production and NOS), the GE 6550A is probably the best sounding for instrument amps, followed by the Svetlana "Winged C". 6550's are also used in many of the popular Marshall amps (although the Plexi types use EL-34's, which is "yet another" type of output tube). The Marshall Major, for instance, runs four 6550's, resulting in a total power output of just over 200 watts. That sounds like a very similar arrangement to your Traynor amp.

Click to expand...

I'm not trying to be a smartazz, or Mr. Knowitall, but the 6550 is pretty similar to the 6L6 and EL34. The big difference with the 6550 is the "cleaner" sound and higher headroom. (I have a 50w Marshall in the basement with 2x6550s as well as a 50w Park with 2xEL34s. I've also owned more than a few 100w Marshalls with 4 6550s.) The other thing about only the Plexis using EL34s, it is the preferred tube for by Marshall. The only reason they changed to 6550s in the mid-70s is because of the lack of availability of good quality EL34s at the time. They pretty much discontinued using the 6550 sometime in the mid-80s.

The 6550 is indeed similar to the 6L6, but the 6550 has much higher power ratings. Kinda like a Chevy 350 is like the 305...same general engine type, only the 350 provides more torque and horsepower.

The 6550 can only be subbed for the 6L6 in certain amps, in part because the filaments draw more heater current (a LOT more current) and many amps don't have a power transformer to handle it; not to mention the bias is completely different, and the output transformer impedance differs somewhat. In my Ampeg V4 the 6550 is commonly subbed for the 7027 (which is in reality a 6L6 with an extra pin out) with only a bias change, but the PT is massive compared to many other amps.

I'm not trying to be a smartazz, or Mr. Knowitall, but the 6550 is pretty similar to the 6L6 and EL34. The big difference with the 6550 is the "cleaner" sound and higher headroom. (I have a 50w Marshall in the basement with 2x6550s as well as a 50w Park with 2xEL34s. I've also owned more than a few 100w Marshalls with 4 6550s.) The other thing about only the Plexis using EL34s, it is the preferred tube for by Marshall. The only reason they changed to 6550s in the mid-70s is because of the lack of availability of good quality EL34s at the time. They pretty much discontinued using the 6550 sometime in the mid-80s.

Click to expand...

Pretty similar in what ways? They're both beam tetrodes and have the same pinout, but the similarities end there. A 6550 can dissipate around 50W while a 6l6 can do about 25W at best. The 6550 is set up to operate at higher plate voltages than the 6L6. They might have the same pinout but they aren't drop in replacements for each other. A 6550 will draw about 2x the filament current of a 6L6. The plate curves and bias requirements are quite different... Not to mention any sonic differences....
Nonsqtr hit the nail on the head.

how easy would it be to change the 6L6's in my Bassman 135 with 6550's?

Click to expand...

Not really much point. You won't get any more power out of the amp (limited by the power supply) and you'd have to mod the bias circuits. The filament windings on the transformer may not be able to supply the necessary current either.